Liquid crystal display (LCD) has many advantages, such as thin body, power saving, no radiation, is widely used in various applications, such as LCD TVs, mobile phones, personal digital assistants (PDAs), digital cameras, computer screens or notebook screens, etc., and plays an important role in the field of flat panel display.
Most of the liquid crystal displays on the market are backlight-type liquid crystal displays, which include a liquid crystal display panel and a backlight module. The working principle of the liquid crystal display panel is to inject liquid crystal molecules between a thin film transistor array substrate (TFT Array Substrate) and a color filter (CF) substrate and apply driving voltages to two substrates to control the rotation direction of the liquid crystal molecules to refract the light from the backlight module to produce a picture.
Due to the optical anisotropy of liquid crystal molecules, there is a problem of color casting while looking the liquid crystal panel in a large viewing angle. In order to solve the problem of color casting in a large viewing angle of the liquid crystal panel, the existed method includes using a multi-domain pixel structure and pre-processing the input data signal voltage by using a color casting compensation algorithm, wherein the multi-domain pixel structure is to divide each sub-pixel in the image pixel into smaller display units, for example, a sub-pixel is divided into a main region and a sub region. The driving voltages of the main region and the sub region are proportional to each other so that the liquid crystal molecules corresponding to the main region and the sub region are deflected to different angles. Therefore, viewing results obtained from different angles could be better. Specific steps for implementing the color casting compensation algorithm include: generating a first display grayscale value and a second display grayscale value respectively according to the original grayscale values of each primary color component of each image pixel of the image to be displayed; using the first display grayscale value and the second display grayscale value to control the display brightness of two sub-pixels of the same color on the liquid crystal panel, respectively, wherein the first display grayscale value is greater than the second display grayscale value, so that the driving voltages applied to the two sub-pixels are different. Accordingly, the liquid crystal molecules of the two sub-pixels are deflected to different angles so that better viewing effects can be obtained by viewing the image at different angles, and the purpose of reducing color casting is achieved.
Wherein, an image is usually composed of a plurality of image pixels, and each image pixel includes three primary color components of red, green and blue. While driving to display an image, the brightness of a primary color component is controlled through providing a grayscale value needed for displaying to each primary color component of each image pixel so that the primary color component displays a corresponded color to display the image. In one image pixel, each primary color component controls two sub-pixels of the same color and adjacent to each other. That is, the red component correspondingly controls two adjacent red sub-pixels, the green component correspondingly controls two adjacent green sub-pixels, and the blue component correspondingly controls two adjacent blue sub-pixels, so that the first display grayscale value and the second display grayscale value generated from the original grayscale value of the red component respectively control the display brightness of the corresponded two red sub-pixels, the first display grayscale value and the second display grayscale value generated from the original grayscale value of the green component respectively control the display brightness of the corresponded two green sub-pixels, and the first display grayscale value and the second display grayscale value generated from the original grayscale value of the blue component respectively control the display brightness of the corresponded two blue sub-pixels. The display brightness of each image pixel is a mixture of the display brightness of the corresponded primary color components, and the display brightness of each primary color component is a mixture of the display brightness of the corresponded two sub-pixels. Generally, in order to keep the mixed display brightness of the two sub-pixels controlled by the first display grayscale value and the second display grayscale value being the same as the display brightness of the two sub-pixels controlled by the original grayscale value, the sum of the display brightness corresponding to the first display grayscale value and the display brightness corresponding to the second display grayscale value is usually set to be twice of the display brightness corresponding to the original grayscale value.
When the input data signal voltage is preprocessed by the color casting compensation algorithm in the existed technologies, the color casting compensation is performed on all the image pixels, the granular feeling is obvious, and the display effect is poor. In fact, when the user watches the displayed image in the side view, the most visible color casting occurs while display the skin color, and the user also pays more attention to the part of skin color of the displayed image.